This invention relates to improvements in the manufacture of can ends to which lining compounds, sealant materials and other coating materials, are applied during the manufacturing process.
In the manufacture of push-in easy-opening can ends of the type described in our Australian Pat. Nos. 444,068, 518,940 and 523,783, a sealant compound, such as a pvc plastisol, must be applied in the regions in which the sheet metal has been severed to ensure that the completed can end is capable of providing an hermetic seal. The sealant material is preferably applied by the method described in our Australian Pat. No. 477,562, and this method, with modifications to the means for pumping sealant through the orifice, is the method used in the commercial production of push-in easy-opening can ends in Australia.
In the conversion of the basic can end shell into a push-in easy-opening can end, the end must be subjected to several die operations as well as a sealant application operation. During the manufacturing process, the ends are supported by a rotary or linear indexing mechanism by means of which the ends are transferrred from one stage to another. The die stations and sealant application station are usually located in a chamber which has relatively confined dimensions.
Where the press carrying the conversion dies and sealant applicator is operational at high speeds (for example from 250 to 300 ends per minute) there is a tendency for the sealant applied by the above described method to spatter slightly. Although the degree of spatter experienced is commercially acceptable, it is somewhat unsightly and wasteful and therefore should be avoided if possible at a relatively low cost.
Since other sealant application methods are likely to be affected in a similar manner, the present invention should not be regarded as being restricted to the particular sealant application method referred to above.
Investigations leading to the present invention involved the use of a linear belt transfer system arranged over a series of die stations and a sealant application station. Observation of the transfer belt during its reciprocating movement between the transfer position and the die station engaging position, particularly near the bottom of the press stroke, indicated that it acted like a diaphragm alternately causing compression and rarefaction of the atmosphere surrounding the die and sealant application stations thereby causing a rapid bidirectional flow of air longitudinally of the die sation chamber. This rapid translational movement of air is believed to cause any strings of sealant connecting the sealant applicator head and the can end to be broken and spattered.
Although the above observations relate to one particular form of transfer apparatus, the invention is equally applicable to other forms of transfer apparatus in which the same problem is found to exist. For example, the invention is also applicable to vacuum assisted transfer mechanisms of the type presently manufactured by Stolle.